The amount of hazardous waste has significantly increased with the growth of chemical industries and the use of their products. The increased toxicity and/or flammability of some of these wastes has also risen. Recognition of the hazardous nature of these materials has lead to the imposition of regulations on their storage and use.
The implementation of some of these safety regulations requires the construction of a specialized, expensive facility for storing toxic and/or flammable materials. These facilities often use masonry construction or are laboriously assembled out of very basic building elements. Once constructed they cannot be relocated. Also, with conventionally built structures it is difficult to inspect and determine that the building would ultimately meet the code standards as regards to fire resistance, secondary containment and structural strength. There is now an industry supplying factory built modular buildings with standard approved designs which conform to all applicable codes. These are shipped essentially complete to the end users facility, freeing the end user from reinventing and obtaining approval for each new facility.
The Factory Mutual Research Corporation, a nationally recognized risk evaluation and prevention company, has now adapted and enforces a generally accepted standard: "Approval Standard for Storage Buildings for Flammable and Combustible Liquids, Class Number 6049." This standard first specifies certain performance standards for the structure. These are:
Resist 90 MPH wind (Commercial requirements have de facto pushed this to 110 MPH). PA1 Resist 250 pounds per square foot floor load. PA1 Resist 40 pounds per square foot snow load. PA1 Provide secondary containment equal to 25% of the liquid capacity of the building. PA1 Resist 100 pounds per square foot internal explosion (for explosion resistant models only). Also provide for explosion venting.
It also recognizes and classifies buildings according to varying levels of fire resistance. These may vary from none to 4 hours as established by test performed in accordance to "ANSI/NFPA 251, Fire Tests of Building Construction and Materials:, promulgated by the National Fire Protection Association.
The assignee of the present invention manufactured and sold a modular building including the prefabricated wall columns, roof and exterior panels similarly constructed to those incorporated in the present invention. These early buildings lacked explosion resistance and fire resistance, which severely limited their application. Factory Mutual would not certify them as appropriate for the storage of Class 1A, or the dispensing of Class 1B, liquids. They could be used for the storage of less flammable liquids, but only if the building were located more than 50 feet from the user's main facility. The present invention addresses these deficiencies, and it is now recognized by Factory Mutual to be explosion resistant, to have a fire resistant wall design at the 2 hour level and to have a fire resistant roof design at the 2 hour level.
Because the original way in which the assignee achieved its fire resistance rating for its wall and for its roof is a significant part of the invention, a brief description of the testing procedure required will now be made. The governing document is ANSI/NFPA 251 or the essentially identical ASTM E119. For the walls, a typical sample the wall design is subjected on one side to a flame with a carefully defined time/temperature curve. Thermocouples on the unexposed side monitor the temperature rise there. After a predetermined time (in this invention, 2 hours) the flame is removed and the wall sample is subjected a strong hose stream to simulate the activities of fire fighters. Passing of the test requires that the temperature rise on the unexposed side during the (2 hour) test be below certain limits. Further, the hose stream cannot punch through the wall sample. If, as is the case with this invention, the wall design is asymmetrical then the test must be repeated with a new sample from the other side. The test for the roof is similar except for these two points: (1) the sample is not subject to a hose stream, and (2) the sample is only tested with flame on the bottom side.
There is a distinction made in fire rated designs between "load bearing" and "non-load bearing" wall designs. Load bearing walls are like the 1st of 2 floors, and bear significant axial loads. These must be axially loaded during the fire test. The present invention uses non-load bearing walls which only need to support themselves and fairly minor roof loads. These were not axially loaded during their test.
The present invention applies in an original way (to be described presently) a common mechanism for rendering a structure fire resistant. That is: to incorporate into the structure significant amounts of gypsum board. Gypsum board contains large amounts of water. In a model of the type to be illustrated in the present application there is about 3000 pounds of water locked up in the gypsum board. As the heat is applied, all the water is progressively turned to steam. That absorbs a large amount of energy, and as the steam dissipates the thermal energy is dissipated with it. It takes over two hours in the present invention to boil all the water away. As long as there is water left, the temperature of the unexposed wall will not rise above 100 degrees centigrade. After the water has been driven from the gypsum board, the board becomes very crumbly and cannot by itself resist the force of the fire hose stream.